Forages and Manure - a match made in heaven? (2014)

S. Bittman and D. Hunt

It’s a most natural cycle. Forages are fed to livestock that produce manure, and manure is returned to the soil to provide the nutrients to produce the next crop. After all, it’s what has happened on pastures and rangelands for millennia.

And there is more for today’s sustainable farmers. Compared to other crops, forages often need a lot of nutrients (N, P, K, S), the actual amounts of each nutrient needed depending on the grass-legume ratio.

And there is a longer growing season, which means opportunities for earlier application, later application and mid-season applications.

Grasses in particular have a ravenous appetite for nitrogen and are well adapted to capture whatever nitrogen is available in the soil – even to excess (hence high feed nitrate levels that sometimes occur).

In our research over many years, we have found that grass systems which include the associated beneficial microbes (such as bacteria, fungi and nematodes) that store and recycle nutrients supported by decaying roots and root exudates are surprisingly protective of nitrogen.

For that reason, and because of their long growing season and continuous ground cover, forages are less subject to nitrate leaching losses and less subject to manure runoff than cultivated crops.

Also, there is less worry with forages about contamination by pathogenic microbes like E. coli, since microbes are very far from the food end-products.

But there are complications – many and indeed serious ones. Let’s begin with grazing animals.